1. Field of the Invention
The present invention relates to a high-frequency input/output feedthrough for a package for housing a high-frequency semiconductor element for the millimeter wave region or the like, and also to a package for housing a high-frequency semiconductor element and using the high-frequency input/output feedthrough.
2. Description of the Related Art
A package for housing a high-frequency semiconductor element houses a high-frequency semiconductor element using a high-frequency signal in the micrometer wave region, the millimeter wave region, or the like, in a hermetically sealed manner. A signal input/output portion of such a package employs a feedthrough structure to which a transmission line such as a microstrip line or a stripline is joined and which is hermetically sealed while a semiconductor element is housed in the package.
An example of the configuration of such an input/output feedthrough is shown in FIGS. 19A, 19B, and FIG. 19A is a plane view and FIG. 19B is a sectional view taken along line Ixe2x80x94I of FIG. 19A, in which lower dielectric substrate 1 is made of ceramics or the like. An upper dielectric substrate 2 is made of ceramics or the like and joined to the upper face of the lower dielectric substrate 1, and serves as a part of a case wall of a package. A line conductor 3 is formed on the upper face of the lower dielectric substrate 1. Side face ground layers 4 are formed on the side faces of the lower and upper dielectric substrates 1 and 2. A bottom face ground layer 5 is formed on the bottom face of the lower dielectric substrate 1. An upper-face ground layer 6 is formed on the upper face of the upper dielectric substrate 2. The prior art of FIG. 7 is the configuration of an input/output feedthrough used for so-called metal wall type packages.
According to this input/output feedthrough, the matching of the characteristic impedance of the line conductor 3 is attained by changing the line width of the portion sandwiched between the lower dielectric substrate 1 and the upper dielectric substrate 2 and corresponding to the stripline, with respect to that of the portions in front and in rear of the portion and corresponding to a microstrip line, thereby realizing low return and insertion losses. When an input/output feedthrough having the bottom face ground layer 5 and the side face ground layers 4 on the sides of the dielectric substrates 1 and 2 is embedded in a cutaway part formed in a metal substrate of the package, the isolation characteristics between the line conductor 3 and a line conductor of another input/output feedthrough which is juxtaposed to the line conductor 3 are improved.
In another input/output feedthrough, a ground pattern is disposed on both sides of a line conductor as shown in FIGS. 20A and 20B. FIG. 20A is a plane view, and FIG. 20B is a section view taken along line IIxe2x80x94II. Referring to these figures, a lower dielectric substrate 7, an upper dielectric substrate 8, a line conductor 9, a bottom face ground layer 10, and an upper-face ground layer 11 are configured in the same manner as the lower dielectric substrate 1, the upper dielectric substrate 2, the line conductor 3, the bottom face ground layer 5, and the upper-face ground layer 6 of FIG. 19, respectively. Ground patterns 12 are formed on the lower dielectric substrate 7 so as to laterally sandwich the line conductor 9. Through conductors 13 are through hole conductors or the like through which the ground patterns 12 are connected to the bottom face ground layer 10. Through conductors 14 are through holes or the like through which the ground patterns 12 are connected to the upper-face ground layer 11. The prior art of FIG. 20 has the configuration of an input/output feedthrough used for the so-called ceramic wall type packages. According to this input/output feedthrough, in the same manner as the input/output feedthrough shown in FIG. 19, the matching of the characteristic impedance of the line conductor 9 is attained so as to realize low return and insertion losses. Furthermore, the isolation characteristics are improved by surrounding the line conductor 9 with the ground patterns 12, the through conductors 13 and 14, the bottom face ground layer 10, and the upper-face ground layer 11.
In each of the high-frequency input/output feedthroughs, the lower dielectric substrate 1 or 7 and the upper dielectric substrate 2 or 8 which constitute the stripline portion are usually made of the same dielectric material and configured as dielectric members having a substantially same thickness.
According to such a high-frequency input/output feedthrough of the prior art, in the region (the microwave region) wherein the frequency is relatively low among high frequencies, the transmission characteristics for a high-frequency signal are excellent because the characteristic impedance of the microstrip line portion is matched with that of the stripline portion.
However, for example, in a higher frequency region wherein the frequency is higher than 30 GHz (the millimeter wave region) there arises the following problem. In order to match the characteristic impedance of the line conductor 3, 9 in the stripline portion with that in the microstrip line portion and further suppress a higher order modes, it is necessary to decrease the thickness of the lower dielectric substrate 1, 7 and additionally, since a width d1 of the line conductor in the stripline portion is very small and an unstable state is brought, it is necessary to set a length d2 of the line conductor 3, 9 in the stripline portion to 1/2n (n is a natural number) of the wavelength of a high-frequency signal to be transmitted via the input/output feedthrough, with the result that the length d2 of the line conductor 3, 9 in the stripline portion becomes very short. Consequently, the strength of the input/output feedthrough part is extremely lowered. Even when the length is designed to be 1/2n of the wavelength, the transmission mode in the stripline portion is substantially different from that in the microstrip line portions in front and in rear of the stripline portion because the input/output feedthrough part has a complex three-dimensional shape and the shape is dispersedly produced. This produces a further problem in that the return and insertion losses are increased and the transmission characteristics for a high-frequency signal are impaired.
The configuration shown in FIG. 8 has further problems in that it is difficult to produce the input/output feedthrough because the small through conductors 13, 14 must be formed in the dielectric substrates 7 and 8, and that, because of the shield due to the through conductors, the return and insertion losses are larger as compared with the case of a planar shield.
The invention has been conducted in view of the above-discussed problems. It is an object of the invention to provide a high-frequency input/output feedthrough having excellent transmission characteristics in which the transmission mode for a high-frequency signal in a portion corresponding to a microstrip line is matched with that in a portion corresponding to a stripline portion to reduce the return and insertion losses.
It is another object of the invention to provide a package for housing a high-frequency semiconductor element having excellent transmission characteristics in which, in an input/output feedthrough part, the transmission mode for a high-frequency signal in a portion corresponding to a microstrip line is matched with that in a portion corresponding to a stripline, to reduce the return and insertion losses.
In a first aspect of the invention, a high-frequency input/output feedthrough comprises:
a) a first dielectric substrate 15;
b) a high-frequency transmission line 19 of narrow width extending on one surface of the first dielectric substrate, the high-frequency transmission line having a first high-frequency transmission line portion 19a and second high-frequency transmission line portions 19b, 19c extending from both longitudinal ends of the first high-frequency transmission line portion, respectively;
c) a pair of first ground conductors 20 of narrow width extending on the one surface of the first dielectric substrate, the first ground conductors being spaced from both width direction sides of the high-frequency transmission line, respectively,
each of the first ground conductors having a first ground conductor portion 20a extending along the first high-frequency transmission line portion 19a and second ground conductor portions 20b, 20c extending from both longitudinal ends of the first ground conductor portion along the second high-frequency transmission line portions 19b, 19c, respectively;
d) a second dielectric substrate 16 for hermetic sealing, overlaid on the one surface of the first dielectric substrate so as to cover the first high-frequency transmission line portion and the first ground conductor portions; and
e) a second ground conductor 17 formed on the other surface of the first dielectric substrate over an region including the high-frequency transmission line 19, the first ground conductors 20, and gaps having widths g1 to g4 between the high-frequency transmission line and the first ground conductors, in a thickness direction of the first dielectric substrate,
the second ground conductor constituting first line means 38 together with the first high-frequency transmission line portion, the first ground conductor portions and the first and second dielectric substrates and constituting second line means 39, 40 together with the second high-frequency transmission line portion, the second ground conductor portions and the first dielectric substrate,
wherein a first width W19a of the first high-frequency transmission line portion is smaller than a second width W19 of the second high-frequency transmission line portion (W19a less than W19),
a first distance G1 between the first ground conductor portions 20a on both sides of the first high-frequency transmission line portion 19a in the width direction of the first ground conductor portions 20a is equal to or smaller than a second distance G2 between the second ground conductor portions 20b or 20c on both sides of the second high-frequency transmission line portion 19b, 19c (G1xe2x89xa6G2) in the width direction of the first ground conductor portions 20b, 20c and
a thickness d16 of the second dielectric substrate is selected to be larger than a thickness d15 of the first dielectric substrate (d16 greater than d15), and the first width W19a and the regions g1, g2 between the first high-frequency transmission line portion and the first ground conductor portions are selected so that a characteristic impedance Z19a of the first line means is smaller than a characteristic impedance 19 of the second line means (Z19a less than Z19), in order to make approximation of a transmission mode of the first line means to a transmission mode of the second line means.
In a second aspect of the invention, the first width W19a and first gaps g1, g2 are selected so that the a ratio Z19a/Z19 of the characteristic impedance Z19a of the first line means to the characteristic impedance 19 of the second line means meets the following relationship:
0.5xe2x89xa6Z19a/Z19xe2x89xa60.9
In a third aspect of the invention, a high-frequency input/output feedthrough comprises:
a first dielectric substrate having one surface where a line conductor and cofacial ground layers spaced at a same distance from both sides of the line conductor uniformly in a longitudinal direction of the line conductor are formed, the other surface where a bottom face ground layer is formed, and side faces where side ground layers are formed; and
a second dielectric substrate joined to the one surface of the first dielectric substrate so as to sandwich portions of the line conductor and the cofacial ground layers between the first and second substrates,
wherein the second dielectric substrate is made thicker than the first dielectric substrate,
the portion of the line conductor sandwiched between the first and second substrates is made narrower than the other portions thereof in width, and
the portions of the cofacial ground layers sandwiched between the first and second substrates project toward the line conductor uniformly in a longitudinal direction of the line conductor so as to be spaced at a same distance from both sides of the line conductor.
In a fourth aspect of the invention, the first dielectric substrate has a dielectric constant ∈r15 and a thickness d15, and a thickness d16 of the second dielectric substrate having a dielectric constant ∈r16 is ∈r15/(2∈r16) or more times the thickness d15 of the first dielectric substrate.
In a fifth aspect of the invention, the thickness d16 of the second dielectric substrate is ∈r15/∈r16 or more times the thickness d15 of the first dielectric substrate.
In a sixth aspect of the invention, heights h1, h2 of the projections toward the line conductor of the portions of the cofacial ground layers sandwiched between the first and second dielectric substrates or the gaps g1, g2 between the line conductor and the cofacial ground layers are ∈r15/(2∈r16) or less times the thickness d15 of the first dielectric substrate.
In a seventh aspect of the invention, the dielectric constant ∈r15 of the first dielectric substrate is smaller than the dielectric constant ∈r16 of the second dielectric substrate.
In an eighth aspect of the invention, an upper ground layer is provided on a surface of the second dielectric substrate of an opposite side to the first dielectric substrate, and side ground layers are provided on side faces of the second dielectric substrate.
In a ninth aspect of the invention, the first and second dielectric substrates are made of one or more materials selected from a group of materials including alumina, mullite, glass ceramics, polytetrafluoroethylene (PTFE), glass epoxy resins and polyimides.
In a tenth aspect of the invention, the line conductor and the cofacial ground layers are made of one or more materials selected from a group of materials including Cu, MoMn+Ni+Au, W+Ni+Au, Cr+Cu, Cr+Cu+Ni+Au, Ta2N+NiCr+Au, Ti+Pd+Au, and NiCr+Pd+Au.
In an eleventh aspect of the invention, a package for housing a high-frequency semiconductor element comprises:
a substrate made of a dielectric or metal, having one surface including a mounting portion on which the high-frequency semiconductor element is mounted;
a frame made of a dielectric or metal, joined to the substrate so as to enclose the mounting portion, the frame being notched to form an input/output feedthrough mounting portion whose side faces and bottom face are electrically conductive;
the high-frequency input/output feedthrough of any one of the above-mentioned constructions, fitted to the input/output feedthrough mounting portion; and
a cap attached to a top face of the frame.
In a twelfth aspect of the invention, a package for housing a high-frequency semiconductor element comprises:
a dielectric substrate having one surface including a mounting portion on which the high-frequency semiconductor element is mounted;
a line conductor formed from a proximity of the mounting portion to a proximity of a periphery of the dielectric substrate on the one surface of the dielectric substrate;
first ground layers arranged from a proximity of the mounting portion to a proximity of a periphery of the dielectric substrate on the one surface of the dielectric substrate so as to be spaced at a same distance from both sides of the line conductor;
a dielectric frame joined to the one surface of the dielectric substrate so that the mounting portion is enclosed by the dielectric frame and portions of the line conductor and the first ground layers are sandwiched between the dielectric substrate and the dielectric frame;
a second ground layer formed on the other surface of the dielectric substrate; and
a connecting conductor layer for connecting the second ground layer to the first ground layers,
wherein the dielectric frame is made thicker than the dielectric substrate,
the portion of the line conductor sandwiched between the dielectric substrate and the dielectric frame is made narrower than the other portions thereof in width, and
the portions of the first ground layers sandwiched between the dielectric substrate and the dielectric frame project toward the line conductor uniformly in a longitudinal direction of the line conductor so as to be spaced at a same distance from both sides of the line conductor.
In a thirteenth aspect of the invention, the dielectric substrate has a dielectric constant ∈r15 and a thickness d15, and a thickness d16 of the dielectric frame having a dielectric constant ∈r16 is ∈r15/(2∈r16) or more times the thickness d15 of the dielectric substrate.
In a fourteenth aspect of the invention, the thickness d16 of the dielectric frame is ∈r15/(∈r16) or more times the thickness d15 of the dielectric substrate.
In a fifteenth aspect of the invention, heights h1, h2 of the projections toward the line conductor of the portions of the first ground layers sandwiched between the dielectric substrate and the dielectric frame or the gaps g1, g2 between the line conductor and the first ground layers are ∈r15/(2∈r16) or less times the thickness d15 of the first dielectric substrate.
In a sixteenth aspect of the invention, the dielectric constant ∈r15 of the dielectric substrate is smaller than the dielectric constant ∈r16 of the dielectric frame.
In a seventeenth aspect of the invention, an upper ground layer is provided on a surface of the dielectric frame of an opposite side to the dielectric substrate, and side ground layers are provided in an interior of the dielectric frame above the connecting conductor layer.
In an eighteenth aspect of the invention, the dielectric substrate and the dielectric frame are made of one or more materials selected from a group of materials including alumina, mullite, glass ceramics, polytetrafluoroethylene (PTFE), glass epoxy resins and polyimides.
In a nineteenth aspect of the invention, the line conductor and the first ground layers are made of one or more materials selected from a group of materials including Cu, MoMn+Ni+Au, W+Ni+Au, Cr+Cu, Cr+Cu+Ni+Au, Ta2N+NiCr+Au, Ti+Pd+Au, and NiCr+Pd+Au.
In a twentieth aspect of the invention, a high-frequency semiconductor apparatus comprises:
a semiconductor element installed in a space on the dielectric substrate of the package for housing a high-frequency semiconductor element of any one of the above-mentioned constructions, enclosed by the frame, the semiconductor element being electrically connected to the input/output feedthrough for high-frequency.
According to the high-frequency input/output feedthrough of the invention, the width w19a of the portion 19a of the line conductor 19 which is sandwiched between the lower dielectric substrate 15 and the upper dielectric substrate 16 is smaller than the width w19 of the other portions 19b, 19c, and the portions 20a1 of the cofacial ground layers disposed on both sides of the line conductor to be spaced at the same distance from both sides of the line conductor are projected toward the portion 19a of the line conductor 19 by the heights h1, h2, respectively, so that gaps g1, g2 (g1=g2)are preserved. Therefore, the electric field distribution in the portion in which the line conductor is sandwiched between the lower dielectric substrate and the upper dielectric substrate and which corresponds to the stripline becomes similar to the electric field distributions in the other portions which are in front and in rear of the portion, in which the line conductor is exposed, and which correspond to the microstrip line. This causes the transmission modes for a high-frequency signal in the two kinds of portions to become similar to each other. Even when the characteristic impedances of the two kinds of portions are different from each other, therefore, return and insertion losses due to a difference of the transmission modes are not produced. As a result, excellent transmission characteristics for a high-frequency signal can be obtained.
According to the package for housing a high-frequency semiconductor element of the invention, the high-frequency input/output feedthrough part is structured by using the above-mentioned high-frequency input/output feedthrough of the invention. In a transmission of a high-frequency signal between a high-frequency semiconductor element housed in the package and an external electric circuit, therefore, return and insertion losses due to a difference of the transmission modes in the input/output feedthrough are not produced. Consequently, a package for housing a high-frequency semiconductor element which has excellent transmission characteristics for a high-frequency signal and which has superior high-frequency characteristics can be obtained.
As a result, According to the invention, it is possible to provide a high-frequency input/output feedthrough in which the transmission modes for a high-frequency signal in a line conductor are matched with each other, thereby reducing the return and insertion losses, and which has excellent transmission characteristics.
According to the invention, it is possible to provide a package for housing a high-frequency semiconductor element in which the transmission modes for a high-frequency signal in a line conductor of an input/output feedthrough part are matched with each other, thereby reducing the return and insertion losses, and which has excellent transmission characteristics.